Spawner Disapearing

This morning at around 4 or 5 a.m. I finally got a spawner. It was a zombie spawner, wish it were pig, and was trying to get the zombies spawn. Unfortunately, there was a server restart a little after I got things going. When I got back on it was gone. It didn't rollback, I know because I was in the same place that I was in before the restart.